The invention relates to a device for centering a plastic web, and more particularly to the centering device for the plastic web so as to be correctly gripped at the opposite side edges thereof by a pair of cramp chains to be brought into the forming machine.
Various articles such as plates, dishes, bowls, buckets, refrigerator linings, bath tubs and the like are formed by feeding plasticized polymer sheet between separated male and female dies and engaging said dies together in the forming machine. The plastic sheet may be formed continuously by the extruder through a slit nozzle of sizes corresponding to the width and thickness of the sheet to be formed. Since the forming operation according to alternate engaging and disengaging of the opposite dies is of intermittent nature, the continuously formed plastic sheet can not be directly fed to the forming machine without providing any particular means for compensating slackening of the continued sheet to be inevitably caused during every forming operation.
In general, the extruded plastic sheet is thus successively cut in a desired length of webs for forming the desired article, which are taken on a pallet to be delivered directly from the extruder or from a warehouse once stored to the forming machine.
The stack of plastic webs, however, is inevitably collapsed to be uneven more or less on the pallet during the delivery. When the stacked webs are automatically taken up as they are one by one by a robot sucking disk carrier, it is often impossible for the pair of cramp chains of the forming machine to correctly grip the webs successively fed from the robot.
Since the industrial robots work just according to the locus previously taught, the article to be processed thereby must be always placed in the correct position. The usual centering devices for substantially flat articles comprise a pair of stoppers to abut on the two adjacent side edges thereof and pair of movable centering members to urges the article at the opposite two side edges toward said stoppers. The movable members are stopped in reply to reaction of abutment on the concerned side edges of the article or detection of the moved stroke of the centering members determined fixedly in advance.
The centering devices of the latter type are not suitable for treatment of the article of which sizes are varied, since many detectors such as limit switches, encoders and the like must be provided so as to cope with such varied sizes. The devices of the former type are not satisfactory since the manufacturing errors in the size is doubled at the two sides of the article on which the movable members abut.
Japanese Utility Model Application laid for early opening (KOKAI) on Dec. 5, 1985 under the number of Sho 60(1985)-183,131 has disclosed the centering device of said former type for substantially flat articles, above all automobile front and rear curved window glasses to be applied with adhesives along the four side edges thereof by the robot applier, which comprises a plurality of vertical bars for supporting said curved glass on the tops thereof, a plurality of pairs of opposite centering members movable longitudinally and transversely, and corresponding numbers of driving means each comprising a central rotor cylinder, a central link lever fixed thereon to be angularly moved, a pair of link arms each pivotally connected with the free end of the central link lever at one end and with said centering member at the other end so that when said rotor cylinder is angularly moved the opposite members are moved toward and apart with each other.
This proposal, however, cannot be used for the plastic web to be correctly gripped by the cramp chains since the centered web must be brought to the cramps of the chains. Futhermore, the proposed device is not desirable due to the rather too complex and strong construction for treating fairly light plastic web, and due to that it can not cope with wider size variation since the length of the central link lever is mechanistically limited.